Process for the production of sheets of cellulose nitrate or cellulose acetate

ABSTRACT

The present invention is directed to a process for the production of sheets of cellulose nitrate or cellulose acetate with sharply defined, differently colored zones which comprises producing a sheet of said material according to the &#39;&#39;&#39;&#39;block method&#39;&#39;&#39;&#39; utilizing pressures and heat, desicating and pressing said sheet and treating the desired zones of the sheet surface with a printing process, thereby applying the desired coloring material to said sheet, said coloring material containing a binder of the same material from which the sheet is produced.

United States Patent [1 1 Stock Aug. 21, 1973 PROCESS FOR THE PRODUCTION OF SHEETS OF CELLULOSE NITRATE OR CELLULOSE ACETATE [75] Inventor: Harald Stock, Oberpleis, Germany [73] Assignee: Dynamit Novel AG, Troisdorf,

Germany [22] Filed: Jan. 28, 1970 [21] Appl. No.: 6,402

[30] Foreign Application Priority Data Feb. 4, 1969 Germany P 19 05 293.8

[52] US. Cl 156/277, 117/38, 156/307 [51] Int. Cl B32b 31/12 [58] Field of Search 156/277, 307;

[56] References Cited UNITED STATES PATENTS 3,255,695 6/1966 Johnson et a1 117/38 X 3,389,029 6/1968 Forman et al. 156/277 X 3,470,054 9/1969 Tyrrell 156/277 X 3,472,802 10/1969 Bownes et al 117/38 X FOREIGN PATENTS OR APPLICATIONS 479,508 0/1938 Great Britain 156/277 851,489 10/1960 Great Britain 156/277 OTHER PUBLICATIONS Yarsley et al., Cellulose Plastics", pp. 97, 98, 206 and 207,1LlFFE Books Ltd. (1964), London, copied in Sci. Lib.: TP 986 A2 436.

Primary Examiner-Benjamin R. Padgett Assistant Examiner-E. A. Miller Attorney-Craig, Antonelli and Hill [5 7] ABSTRACT 8 Claims, 2 Drawing Figures PAIENTEDAusm ms 3.753325 INVENTOR HARALD STOCK ATTORNEYS PROCESS FOR THE PRODUCTION OF SHEETS OF CELLULOSE NITRATE OR CELLULOSE ACETATE BACKGROUND OF THE INVENTION The present invention relates to a process for the production of sheets from Celluloid (cellulose nitrate) or cellulose acetate with differently colored zones which are sharply defined on all sides. l

Sheets or strips of Celluloid" or cellulose acetate are used for the manufacture of spectacle frames, combs, filter plates, scales (graduated elements), templates, or other articles. These semifinished products are employed in one color, namely transparent or opaque or in covered colors, as well as twoor multicolored arrangements. They can be in the form of socalled inlays (embeddings), for example, Havana or agate, and as twoand multiple-layered laminations.

Heretofore, the sheets have been produced in accordance with the block method, wherein a solventcontaining plastic (synthetic polymeric material) mass is boiled into blocks under pressure at an elevated temperature. Inlays are obtained by inserting colored components in the strip or cube-shaped plastic, boiled mass, in accordance with specific empirical values, and compressing the composite at an elevated temperature. This procedure is repeated twice to three times, depending upon the pattern.

For two and multiple-layered laminations, the individual sheets are glued to one another in a partially or completely desiccated condition, with the aid of solvents.

The previously employed inlay technique does not make it possible to produce sheets in a reproducible manner in flawless quality having differently colored zones which are sharply defined on all sides. Distortions and displacements are frequently produced, especially due to the heating of the entire mass under pressure, following the manually conducted inlay of differently colored components.

SUMMARY OF THE INVENTION An object of the present invention is to avoid the prior art disadvantages in producing sheets of Celluloid or cellulose acetate.

Another object of the present invention is to provide a process for producing sheets of cellulose acetate and cellulose nitrate with differently colored zones which are sharply defined, true in size, reproducible, of flawless quality and inexpensive to produce.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; It should be understood, however, that the detailed description has specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Pursuant to the present invention, it has beenfound that the abovementioned disadvantages may be eliminated and a much improved process for manufacturing sheets of Celluloid" or cellulose acetate with sharply defined, differently colored zones may be obtained wherein the sheet produced in accordance with the so called block method, with the useof pressure and heat,

is desiccated (dried) and pressed, and thereafter, the

desired zones of the sheet surface are treated with an application of color (ink), by means of a printing process, for example a screen-printing processThe coloring material contains as a binder, the same cellulose nitrate or acetate of which the sheet has been produced. Also, the sheet is made with the use of solvents which exhibit good solubility properties with respect to the material to be printed. I

With the aid of the process of the present invention, it is possible, in an effective and economical manner, with a relatively small amount of work, to produce semifinished articles which permit the achievement of highly fashionable effects, and new design and form aspects. The present process also makes it possible to exploit technical possibilities which heretofore could not be realized, or were feasible only at a substantially higher expenditure of work when using the conventional methods of manufacture.

By means of inks and of the present invention, well drying and laminatable prints can be obtained, whereas the silk-screen printing inks, which are available commercially and which are produced with polyvinyl compounds, cannot be utilized due to plasticizer migration (seeping). Thus, the printed'on ink becomes smeary and during the subsequent laminating procedure there is no or very little adhesion in the printing zone. The printing inks of the present invention can contain a variety of pigments, either individually or in combination.

Exemplary of the printing inks which can be used in the present invention included a composition containing about 10 cellulose acetate, about 40% acetone,

about 10% diethyl phthalate and about 40% methyl glycol acetate. Depending on the dyestuff, about 2% of a pigment or soluble dye can be added to the composition.

.Special effects can be obtained by selecting the colors in accordance with the purpose for which the article will be employed. Thus, the so-called bleeding dyestuffs now show gentle blending effects.

In order to protect against surface damage during processing and use, a protective plate of desired thickness is generally laminated to the sheet in the press. In this connection, the otherwise customary laminating method, that is, operating with solvents, cannot be utilized, since the print will become partially dissolved and smear. However, if employing, in accordance with a further feature of the present invention, a so-called adhesive film having a high plasticizer content, as it is used in some cases for the lamination of cellulose acetate plates, a sharply contored print is retained, which print is protected by the eminently adhering protecting film laminated thereon. The plates thus withstand the customary processing stresses, such as stamping (punching), bending, and milling.

Exemplary of the adhesive films which can be used in the present invention include a composition comprising about 50-60% cellulose acetate and about 40-50% of plasticizer mixture of phthalic acid ester and phosphoric acid ester.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE According to FIGS. 1 and 2, triangular or rectangular zones 1 are printed on a 5 mm thick blue-transparent plate of optical cellulose acetate, in a conventional manner by means of the silk-screen printing process. A screen-printing ink colored with blue pigments and containing cellulose acetate is employed. After the print has dried, an adhesive film having a thickness of about 0.1 mm, as well as a blue-transparent cellulose acetate plate having a thickness of about 0.9 mm. are placed thereon. The bonding by lamination is conducted at temperature of about 140 170C., preferably about 160C, and under a pressure of 30 atmosphere gauge in a multilayer plate press. From the plate, the spectacle frames 2 or also other configurations can then be stamped out.

A description of the block method for producing a sheet of material can be found of pages 174-179 of Plastics Handbook Ill, Modified Natural Substances by Carl-Hanser Publishers, Munich. Another published description of the block method can be found in Cellulose Plastics, Yarsley, London lliffe Books Ltd., 1961, pp. 97-98. In particular, this description is as follows:

The block process for making sheet material was originally developed in the cellulose nitrate industry and later applied to cellulose acetate. It is particularly suited to the production of sheets over 0.010 in. thick. In this process, which is in some ways analogous to the wet process for compounding cellulosic plastics, a wet mix (i.e. containing volatile solvent) is prepared by mixing cellulose acetate flake, plasticisers, and solvents in a kneader of the Werner-Pfleiderer type. Colourants may be added at this stage. A typical formulation for a clear sheet is as follows:

Cellulose acetate 100 parts by weight (52-54% acetic acid) Dimethyl phthalate Triphenyl phosphate 23 parts by weight 7 parts by weight A small proportion of water may also be included.

The extremely viscous mixture is filtered by being forced under high pressure through filtering screens. This operation is performed by a stuffing press, which consists basically of a cylinder to contain the viscous mass and a hydraulically-actuated ram to apply pressure,

After filtration, the composition passes to a pair of warm mixing-rolls, on which rolling is carried out until the solvent content is reduced to about 10 percent. The solvent vapour removed during this operation is ducted away for recovery. When the mass has reached this stage, it is cut off the rolls as a hide about 1 in. thick. This hide is laid on a thick steel base-plate which is usually grooved or otherwise indented to enable the plastic to make a good key" on to the plate during the pressing operation.

Sufficient hides from the mixing rolls are stacked on top of each other to form a block 56 in. thick and about 52 in. long by 22 in. wide. This block, on its baseplate, is inserted into a hydraulic press, a polished steel plate, placed upon the top of the block, and a pressure of about 1 ton/in. applied, while maintaining the platens at a temperature of about 95C. Heating under pressure is continued for several hours, and the press is then cooled, still holding the pressure. Complete cooling of the block is very important, and may require 6 h or more in the press.

The block is next transferred to an automatic slicingmachine, being held on the bed of the machine by means of the base-plate which has become firmly welded to the block during the pressing operation. The height of the knife of the slicing machine is set at the start of the slicing operation and descends automatically for a predetermined distance after each cut, thus producing sheets of substantially the same thickness.

The sheets produced in this manner still contain an appreciable amount of volatile solvent, which is removed by storing them in warm seasoning-rooms. The final operation is that of polishing to remove the knife marks. The sheets are placed between highly polished nickel plates, and pressed in a hydraulic press at about C. under a pressure of 1 ton/inf. After applying pressure for a few minutes, the press is cooled, still under pressure. Multi-daylight presses are normally used, enabling a number of sheets to be treated at the same time. If desired, matt or embossed surfaces can be produced by this operation. When cold, the sheets are removed from the press and passed to storage.

Variegated colour effects can be produced by forming a block with alternate hides of different colours. After slicing, the sheets are trimmed to size, restacked on end in the desired arrangement, and rewelded into a new block, from which multicolour sheets may subsequently be sliced.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be included.

WHAT IS CLAIMED IS:

1. In a process for the production of sheets of cellulose nitrate or cellulose acetate having differently colored zones wherein a desiccated and pressed sheet of cellulose nitrate or cellulose acetate is produced, desired zones of the surface of the sheet are printed with a coloring materiaL and thereafter the surface of the sheet having said colored zones thereon is laminated with at least one convering layer of thermoplastic material, the improvement which comprises applying the coloring material to said sheet of cellulose nitrate or cellulose acetate by a printing process, said coloring material containing a binder which is made of the same material as said sheet and a solvent which exhibits good solubility with respect to the material forming said sheet; drying the resulting printed sheet to remove solvent therefrom and placing an adhesive film containing cellulose acetate and a high content of a plasticizer for said cellulose acetate thereover and applying pressure and heat to the adhesive film coated printed sheet laminate.

2. The process of claim 1, wherein the printing process utilized is silk screen printing.

3. The process of claim 1, wherein the adhesive film is further laminated with a thin transparent cellulose acetate sheet by the additional use of pressure and heat.

4. A process for the production of plates of cellulose acetate having sharply defined differently colored zones which comprises producing a thick bluetransparent plate of optical cellulose acetate; treating desired zones of said plate with a printing ink colored with blue pigments containing cellulose acetate as a binder therefor, a solvent for cellulose acetate, and a small amount of a plasticizer for cellulose acetate; drying the treated plate; placing a thin adhesive film consisting essentially of 50 to 60 percent by weight of cellulose acetate and 40 to 50 percent by weight of a plasticizer for said cellulose acetate thereon; applying a blue-transparent cellulose acetate plate having a thickness substantially less than that of the printing plate to said adhesive film to thereby form a composite plate product; and bonding said composite product at a temperature of about 140 to 170C. and at a pressure of product is bonded at a temperature of about 160C. 

2. The process of claim 1, wherein the printing process utilized is silk screen printing.
 3. The process of claim 1, wherein the adhesive film is further laminated with a thin transparent cellulose acetate sheet by the additional use of pressure and heat.
 4. A process for the production of plates of cellulose acetate having sharply defined differently colored zones which comprises producing a thick blue-transparent plate of optical cellulose acetate; treating desired zones of said plate with a printing ink colored with blue pigments containing cellulose acetate as a binder therefor, a solvent for cellulose acetate, and a small amount of a plasticizer for cellulose acetate; drying the treated plate; placing a thin adhesive film consisting essentially of 50 to 60 percent by weight of cellulose acetate and 40 to 50 percent by weight of a plasticizer for said cellulose acetate thereon; applying a blue-transparent cellulose acetate plate having a thickness substantially less than that of the printing plate to said adhesive film to thereby form a composite plate product; and bonding said composite product at a temperature of about 140* to 170*C. and at a pressure of about 30 atmospheres.
 5. The process of claim 4, wherein the thick blue-transparent plate of optical cellulose acetate has a thickness of 5 mm, the adhesive film has a thickness of about 0.1 mm, and the thin blue-transparent cellulose acetate plate has a thickness of about 0.9 mm.
 6. The process of claim 4, wherein the solvent for cellulose acetate includes acetone and methyl glycol acetate.
 7. The process oF claim 4, wherein the plasticizer for cellulose acetate includes a phthalic acid ester.
 8. The process of claim 4, wherein said composite product is bonded at a temperature of about 160*C. 